TDI conversion on a \'91 Golf Gti
TDI from an A3-chassis into an A2-chassis? It can be done and it HAS been done, but don't underestimate what's involved to do it right. You need the entire driveline including the tranny, you need to figure out how to make the TDI's cable shifter work, you need to figure out how to make the TDI's hydraulic clutch and drive-by-wire accelerator work, you need to make all the electronics work, you need to find a place for the intercooler and make the intake and exhaust systems work, AND since you are working with a vehicle that originally had a gasoline engine, you need to change a bunch of stuff in the fuel system, AND figure out how to make the tachometer work since a TDI doesn't have ignition coils to operate a tach with. And that's not even including all the nitty-gritty details that you'll run into.
Search the forums, it's been discussed before. I REPEAT ... it can be done and it HAS been done several times, but it's neither easy nor inexpensive.